Can't suggest exactly where the ends are, but purple's usually fibre optic cabling / data cabling (more often fibre and unlikely to be copper if it runs for more than a couple of miles, so I'd guess fibre), green's usually telephony or more data cabling and black's usually low-voltage power (240/415) so assuming the ducts were laid during the last 5 years...
Looking on a map, the route you suggest *could* be from the M1 to the A1M, the Highways Agency could have laid the ducting for the NRTS (National Roads Telecommunication System) which uses plenty of cameras, Cellstack digital video codecs and Alcatel gigabit ethernet switching over fibre for the digital motorway safety cameras (and yes, they are *safety* cameras), for the proposed hard-shoulder use - idea is to spot broken-down vehicles on the hard shoulder and use adaptive gantry signs to divert traffic off the hard shoulder when it's being used during traffic peaks, the roadside 'phones may be in the green duct, power for repeaters etc. in the black? There are only a handful of Highways Agency Regional Control Centres (mainly on industrial estates at the confluences of motorways - follow one of the "fake cop" HA
4x4s at tea-break to discover your nearest!) so the infrastructure reaches out quite a way, and it's a fairly resilient network with plenty of redundant routes for "survivability". This is one reason there have been so many seemingly unrelated-to-carriageway road works over the last few years, laying duct, building the wayside equipment huts etc.
A note for the paranoid: Yes, it'll eventually (possibly already) cover the majority of the motorways, but the one time I saw it used for "surveillance" the CID couldn't tell one white transit van from another! I heard a rumour that the stored video (being digital personal data?) is subject to the Data Protection Act, so one has the right to request copies of one's journey along the motorway, too... And that this has prompted the swift routine deletion of the video to avoid "adminstrative costs"!
Underground piping/ducting/conduit seems (by observation) to follow a code if laid relatively recently
Red -power Blue -water Yellow -gas Green - telecoms Purple - motorway CCTV (and maybe non motorway too?) Black - possibly drainage of some sort - I've seen it used for surface water rather than foul drains Brown -underground domestic foul and surface water - not sure about larger services Grey - above ground domestic waste and foul drainage
Your example of multiple colours laid at the same time would suggest a huge degree of coordination (quite out of character) between the utility companies which makes me think it might of been for some other purpose.
Some years ago I had a job interview with trafficmaster. Their roadside cameras anonymised the data before it left the camera - replaced the reg plate with a non-unique 5 digit code. They didn't want to have to deal with privacy issues - their interest was monitoring traffic flows by measuring journey-time between fixed cameras - and simply discarded the odd bit of erroneous data where 2 cameras randomly selected the same tag in the same time window. This meant data could be sent wirelessly and unencrypted.
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